use rubocop
fix coding style
don't run rubocode on ruby 1.8.7
don't install rubocop under ruby 1.9.2
use single-quate if don't need double-quate
don't fail test even if rubocop detects some offence
follow Ruby Style Guide for some points
remove duplicate spec
Merge pull request #41 from muratayusuke/feature/rubocop

Feature/rubocop